Low voltage relays

[DarrenSV650S]

Originally Posted by tigersaw

Kind of. The timer chip on the board needs a -ve going trigger, so depends on how the LED is driven, switched earth or switched +3v. If switched earth its straightforward, if +ve, then it needs a transistor added as an inverter.
Going to order the board and a mini siren and have a fiddle.

When I tested the green LED it was flashing (finding a signal) and the reading kept jumping up and down. When it found a signal it settled on 3.3V

Don't understand why it needs an inverter

[tigersaw]

Originally Posted by DarrenSV650S

When I tested the green LED it was flashing (finding a signal) and the reading kept jumping up and down. When it found a signal it settled on 3.3V

Don't understand why it needs an inverter

The LED could have a permanent +3.3V on the anodes, and illuminated by grounding the cathode - this is a common way of driving LEDs from IC's.

Equally it could have a perminant earth, and illuminated by sending +3.3V. In this case the 555 timer chip cannot be triggered directly, but adding a simple transistor inverter would sort it out.

Either way would read the same from a meter.

I have just ordered the timer circuit, I'll experiment when it comes.